Scientists and transhumanists are still groping in the dark when they make theories about what a thought is or what a person is. In particular, the more they insist on limiting their theories to our current understanding of matter and the brain, the more wooden and false those theories become. You are probably better off thinking that a person is an energy vortex in the quantum fields of the brain, and that a thought is produced in the vortex by those electrical impulses - and even better if you can think of that as just a science fiction image of something we don't understand yet, rather than the literal truth.

One virtue of this "vortex" picture is that it pictures a person as a single whole. If a person is to live, the vortex has to survive. Maybe you could record brain activity, then start up a new vortex (however that is done) and induce similar experiences and thoughts by playing back the recording; but if you go by physical continuity, that is a new person, not the old one.

Outer space is the traditional transhumanist answer to the tension between infinite life extension and a finite Earth. But no death, ever, is a very tall order. Things break in the physical world. In the short term, our experiments in imitating and rejuvenating human beings are likely to produce entities that are more brittle than natural humans, and that will exhibit a disturbing deficit of humanness in some way. And there will even be technological subcultures that embrace that less-than-humanness as "good enough" - so strong is the desire for more life. Just as you have clung to the idea of an afterlife, others will cling to a particular technology or philosophy.

Life is tragic and mysterious, but the idea that death makes it genuinely unbearable is rare, and rarely sticks around in a person's mind. The will to survive keeps people at their jobs (with a lot of moaning and bitching), and the desire for sex and for children keeps them reproducing, and apparently that's enough to have kept the human show on the road. It's not as if we're all still here because someone once figured out an actual reason why it makes sense to keep going, or someone seriously calculated that the good of continuing outweighs the bad. Perhaps it will all resolve, a little further down the line; we'll have the power to change things, and the knowledge to know what we're doing. Or perhaps that hope will be dashed too.